CHAPTER III 



THEIR RELATION TO PLANTS AS DESTROYERS 



While, as has just been shown, there is a mutual 

 interdependence of plants and insects in which both 

 may be benefited, or if one is harmed, the benefit 

 derived is so far in excess of the injury suffered that it 

 does not count against the value of the relation, there 

 is also a kind of dependence in which the insect gets 

 all the benefit, and the plant all the injury. 



A vast number of insects depend absolutely upon 

 plants for their very life and give nothing at all in re- 

 turn: they are destroyers pure and simple, using the 

 plant tissue as food, as material to supply protection, 

 or as a habitation. But the amount and character of 

 the injury vary enormously and may either be a neg- 

 ligible incident in the life of the plant, or form the 

 principal check to its growth or cultivation. 



We may dismiss with no more than a mere mention 

 that vast horde of insects that gets into plants when 

 they are dead and begin to disintegrate. Nature dis- 

 likes dead organic matter, and when a tree or plant 

 is dead or dying, or when decay begins in a sappy fruit 

 or fungus, there are insects among other agents ready 

 to reduce it to that inorganic condition from which it 

 originated. While the actual death of a diseased or 

 weakened tree is often hastened by such insects, they 

 can hardly be said to be enemies in the direct sense ; but 

 scavengers, ever ready to begin their office and fostering 

 the condition in which it becomes their legitimate prey. 



Beginning with the simplest order, the Thysanura, 

 we find few plant destroyers among them. Originating 



